With the popularity of the computers and the consumers' electronics, various electronic gadgets are becoming a necessity in our daily life. The electronic gadgets contain IC (integrated circuits) chips, such as bottom terminal components (BTC). BTC is getting more and more popular with its high connectivity speed. However, void issues at the central ground pads are problems for the BTC and other computer chips that are attached to printed circuit boards (PCB). For example, a quad flat no-leads package (QFN) from automotive industry has a HiP (Head in Pillow) phenomenon with an occurrence of 90% of field failure in one pin connector, which generally result from the void issues.
Typically, flux is trapped underneath the bottom internal components among other SMT (surface-mount technology) parts in the reflowing process (e.g., SMT soldering). The amount of flux in the paste is around 11% of the total paste amount (in weight). Sometimes, the amount of flux applied is too much and the gases generated in the soldering process are often trapped underneath the components and pads affecting the reliability of the soldering joints. Voids generated by the excess flux and the gases affect mechanical properties and reduce the integrity of the solder joint. Some experiments show that the components and/or computer chips can be lifted by the gases close to 4 mils, which can stress the solder joint in formation between the components and the signal pins.
FIG. 1 illustrates a typical semiconductor assembly having a BTC 101 on a PCB 102. In a typical PCB of SMD pad (solder mask defined) 112 and a NSMD pad (non solder mask defined) 114, flux starts to move and evaporate after the paste reaching 183° C. in a soldering process. The flux entrapped underneath the BTC evaporates and generates gases when heat increases. The flux and the gases try to find a way out. However, the resin seal the external edges (between the solder mask damp 120, 122, 116, and 118 (collectively solder mask damp 124) and the bottom side of the BTC devices 104 and 106) forming a confirmed space 108 and 110. When the gases increase in volume, the devices 104 and 106 are lifted by the gases. In some cases, the devices 104 and 106 can be lifted close to 4 mils, which cause stress to the solder joint in formation between the components and the signal pins. The flux movement starts to decrease as soon as the temperature goes down.